Electroless plating system



United States Patent 3,379,556 ELECTROLESS PLATING SYSTEM Eraldo M.Chiecchi, Redwood City, Calif., assignor to Ampex Corporation, RedwoodCity, Calif., a corporation of California No Drawing. Filed Feb. 24,1965, Ser. No. 435,062 10 Ciaims. (Cl. 117-47) This invention relates toelectroless plating wherein metal is plated on a nonconductive surfaceand, more particularly, relates to the employment of Werner-typechromium complexes to sensitize a surface for such plating.

In the past a number of electroless plating methods have been proposed,but such methods have always required extensive pretreatments such assealing, sandblasting, etching, and the like, to enhance the chemicalbond between the metallic substance and the nonmetallic substrate. Thesemethods have required special machinery and long processing times andhave thus increased the cost of such plating.

According to the present invention, these extensive pretreatments areeliminated by employment of Werner-type chromium complexes which arepolymerized on the nonconductive surface and which are reactive towardthe usual sensitizers and activators used in electroless plating. By

Werner-type chromium complexes is meant those compounds wherein atrivalent nuclear atom of chromium is coordinated with a carboxylicacido group to form a cyclic complex. Suitable Werner-type complexes foruse in the present invention therefore have a trivalent nuclear chromiumatom with an organic acido group complexed therewith. In accordance withthe present invention suitable complexes include methacrylato chromicchloride, acrylato chromic chloride, resorcylato chromic chloride,benzato chromic chloride, palmitato chromic chloride, stearato chromicchloride, and the like. The acido radical may be substituted with othergroups, such as alkyl radicals, oxyalkyl radicals, amino radicals, andthe like.

In carrying out the present invention, the nonconducting surface to beplated is first coated with a solution of a chromium complex and thecomplex polymerized. The complex may be an aqueous solution or it can bean organic solvent, such as methanol, propanol, acetone, isopropanol,butanol, and mixtures thereof. Concentration of the chromium complex inthe solvent can vary within wide limits and it has been found thatsolutions containing 150% of solids are useful in carrying out thepresent invention. The chromium complex may be applied by dipping,coating, spraying, brushing, or similar treatment. After the article tobe plated is wet with the chromium complex, the complex is polymerizedeither by drying the complex or by increasing the pH or both. Generallyit is preferred to increase the pH, although with some materialsincreasing the pH would destroy the substrate in which case drying alonewould be used. Suitably, the pH of the diluted chromium complex israised to about 3 to 5 with the addition of a base, such as ammonia,pyridine, hexamethylcne tetramine, morpholine, trimethylamine,piperidine, sodium hydroxide, or even with weak acid salts, such assodium carbonate, or sodium formate.

Drying of the complex can be accomplished by any suitable means, such asordinary air drying at normal room temperature, oven or hot air dryingat temperatures of from 40 to 150 C., infrared drying, induction heatingor the like. After drying, a further washing of the treated surface withwater, followed by a second drying is frequently employed to increasethe effectiveness of the complex, After treatment with the chromiumcomplex, the substrate is treated with a sensitizer, and then with anactivator, and is then placed in an electroless plating solution whichcontains a salt of a desired metal to be plated together with a reducingagent, such as a sugar or formaldehyde, or the like. Suitablesensitizers are materials which are readily oxidized and are well knownto those skilled in the art, and the particular sensitizer chosen willdepend upon the metal to be deposited and the electroless solution.Typical sensitizers include SnCl Sn(BF TiCl AgNO hydroquinone and HBF towhich may be added HQl, NaOH, NaCl, H SO NH OH, and the like. Suitableactivators are also well known in the art and are salts of the noblemetals such as platinum, palladium, gold and silver.

Substantially any nonconducting surface may be plated with the processof the present invention, including ceramics, vitreous masses, glass,cellulose in such forms as wood, paper, cotton, rayon and celluloseacetate, synthetic high molecular weight polymers, wool, silk,proteinaceous materials, such as gelatin coatings, leather, and thelike.

It will be understood that the invention is one of broad applicabilityand that the following examples are for purposes of illustration only.

Example 1.-Two strips of Du Pont Leader film (polyester) were coated bydipping in solutions of betaresorcylato chromic chloride supplied by E.I. du Pont de Nemours & Co. The solution as supplied had a solidscontent of about 3% and a pH of 1. The solvent was isopropanol.

In one solution the pH of the chromium complex was raised to 4 by theaddition, under agitation, of a 1% aqueous ammonium hydroxide solution.

In the other, the pH was kept at the original value but was diluted withwater at the ratio 1:3.

The samples were dried in an air circulating oven for 3 minutes at 606-5C., washed with water, dried again and immersed in a stannous chloridesensitizer solution for 3 minutes and washed with water. The stannouschloride solution had the following composition:

SnCl -2H O g HCl (36%-38%) cc 10 H O cc 250 Next the strips wereimmersed in a palladium chloride activator solution containing:

PdCl, g 1 HCl (36%38%) cc 10 H O cc 1000 for 2 minutes, washed withwater and immersed in the following solution of nickel:

Glycolic acid (Technical 70%) g 61 NaH PO -H O g 15 NiCl '6H O g 30 NaOHto bring the pH of the solution to 6 H O q.s. 1 liter and maintained at85 C.

Sound, uniform metallic nickel started to deposit in 5 minutes on bothsamples.

Example 2.-A strip of cellulose acetate motion picture film was coatedwith a stock solution of beta-resorcylato chromic chloride, processed bydrying, sensitizing and activating as in Example 1 and immersed in thefollowing electroless copper solution:

NQKC4H4O6AHZO gr NaOH gr 50 CLISO4.5H2O gr Aerosol OT Aq (Dioctyl sodiumsulfosuccinate) percent .005 H O qs. 1 liter.

One part of this solution was diluted with 1 part of water: for every 20cc. of copper solution, 1 cc. of a 3 37% solution of formaldehyde wasadded as a reducing agent.

Sound metallic copper started to deposit in five minutes.

Example 3.-Two strips of a Teflon (polytetrafiuoroethylene) film werecoated, one with a solution of betaresorcylato chromic chloride as inExample 1 and the other with a stock solution of p-amino benzoatochromic chloride. The latter was supplied as a 3.15% solids solution inisopropanol with a pH of 0.8.

Both samples were dried at 90-110 C. for 3 minutes, washed, dried,immersed in stannous chloride and palladium chloride solutions asindicated in Example 1, washed and immersed in the nickel solution ofthe same example at the same temperature. After 15 minutes, sound,uniform metallic nickel started to appear on both samples.

Example 4.A strip of cellulose acetate film was coated with a stocksolution of 3,4,5 trimethoxy benzoato chromic chloride in awater-ethanol solvent. The solution contained 1.3% solids and had a pHof 1.2. The sample was treated with the same process and in the samebaths as is described in Example 1 and uniform, sound, metallic nickelstarted to deposit in minutes.

Example 5.A strip of cellulose acetate film was coated with a stocksolution of beta-resorcylato chromic chloride, processed as in Example 1and immersed in an electroless copper solution as follows:

NaKC H O:4H O "g-.. 170 NaOH g 50 CuSO .H O g 35 AEROSOL OT 75% Aq.percent .005 H O qs. 1 liter.

and mixed in the ratio of 20 to 1 with a 37% solution of formaldehyde.Sound, metallic copper started to deposit in 5 minutes.

Example 6.-Two strips of polyethylene film were coated with a solutionof beta-resorcylato chromic chloride. One sample was heated for minutesat 80-90 C. in an air circulating oven. The other was heated at the sametemperature for 3 days. Both were washed, dryed, in the same manner,sensitized with the stannous chloride solution and a palladium chloridesolution of Example 1 and then immersed in the copper solution ofExample 5. Uniform, sound metallic copper started to deposit in 5minutes.

Example 7.Two strips of a Teflon film were coated, one with a solutionof beta-resorcylato chromic chloride and the other with a stock solutionof p-amino benzoato chromic chloride. Both samples were dried at 90-110C. for 3 minutes, washed, again dried, and then immersed in stannouschloride and palladium chloride solutions as indicated in Example 1. Thestrips were washed and immersed in the nickel solution of Example 1 atthe same temperature. After minutes, sound, uniform metallic nickelstarted to appear on both samples.

Example 8.-Two Vector Boards (phenolic plastic) were coated with a stocksolution of beta-resorcylato chromic chloride. The samples were driedfor /2 hour at 110 C., washed, again dried, and then immersed in thestannous chloride and palladium chloride solutions of Example 1. Theywere then washed and immersed, one in the nickel solution of Example 1,the other in the copper solution of Example 5. Sound, metallic, uniformnickel and copper were obtained on the respective boards.

Example 9.-Two phenolic printed circuit boards were coated and treatedas the Vector Board of Example 8. The same result was obtained.

Example 10.-The proteinaceous part (i.e. emulsion) of two KODAKAerographic safety film strips were coated with a stock solution ofbeta-resorcylato chromic chloride. One sample was dried at 60-65" C. for5 minutes. The other was dried at room temperature. The samples werethen washed in water and dried. The sample dried at 60-65 C. wasimmersed in the stannous chloride and palladium chloride solutions ofExample 1. The other was immersed in only the palladium chloridesolution of Example 1. The strips were next washed and immersed in thecopper solution of Example 5. Sound, metallic uniform copper wasobtained on both samples.

Example 11.A strip of cellulose acetate was coated with thebeta-resorcylato chromium chloride stock soluiton of Example 1. Thestrip was dried in an air-forced oven at 60-65 C. for 5 minutes, washed,dried, and then immersed in the palladium chloride of Example 1 for 5minutes. After washing, the strip was immersed in the nickel bath ofExample 1. Sound, metallic uniform nickel started to deposit in 15minutes.

Example 12.-A strip of cellulose acetate was coated with a stearic acidchromium chloride complex solution diluted with 50% water. The samplewas dried for 3 minutes at C., washed, again dried at the sametemperature, and immersed in the palladium chloride solution ofExample 1. The strip was then washed and immersed in the copper solutionof Example 5. A copper film having a resistance of 1.5 ohms per squarewas obtained in 20 minutes.

Example 13.The Nylon (polyester) portion of a probe holder was coatedwith a stock solution of 3,4,5- trimethoxy benzoato chromic chloride atpH ca. 4 in a water-methanol. The sample was dried for 3 minutes at 110C., washed, dried, immersed in the stannous chloride solution of Example1, washed, and then immersed in the palladium chloride solution of thesame example. The sample was then washed and immersed in the nickelsolution of Example 1. Sound, metallic, uniform nickel started todeposit in 20 minutes.

Example 14.Ar1other Nylon holder was coated with a stock solution ofbeta-resorcylato chromic chloride. The sample was dried for 10 minutesat C., washed, dried, and then immersed in the palladium solution ofExample 1. The sample was then washed and immersed in the nickelsolution of the same example. Sound, metallic, uniform nickel started todeposit in 20 minutes.

Example 15.A stock solution of p-amino benzoato chromic chloride wasdiluted with water in the ratio of 1:1 in which 0.05% a Aerosol OT 75%Aq. was dissolved. A strip of a Teflon film was coated with thissolution, dried for 10 minutes at 110 C., washed, dried again andimmersed in the palladium chloride solution of Example 1 for 5 minutes.The sample was then. washed and immersed in the copper solution ofExample 5. A copper film with a resistance of 1.2 ohms per square wasobtained in 20 minutes.

Example 16.A strip of safety motion picture film was coated with a 4%solution of p-amino benzoato chromic chloride in isopropanol having a pHof l. The sample was dried at 110 C. for 3 minutes, washed, dried againat the same temperature and immersed in the palladium chloride solutionof Example 1. The sample was then washed and immersed in the followingnickel bath:

Nickel hypophosphite g 26.7 Boric acid g 1.2 Ammonium sulfate g 2.6Sodium acetate g 4.9 pH 5.5-6.0 Water q.s. 1 liter.

It was found that at 21 C. the deposition of Ni on the sample was veryslow and a very good nickel film was obtained in 20 minutes when thenickel bath temperature was increased to 4060 C.

Example 17.A strip of cellulose acetate safety film posited over thesample by eelctroplating nickel solution.

Example 18.-A strip of polyethylene film was coated with the samesolution of Quilon C used in Example 17. The sample was dried at 110 C.for 5 minutes, washed, dried immersed in the stannous chloride solutionof Example 1 for 3 minutes, washed, immersed in the palladium chloridesolution of the same sample for 5 minutes. Subsequently, the sample waswashed and immersed in the nickel bath, described under Example 15, keptat 40 C. for 15 minutes. Metallic nickel was deposited.

Example l9.-A piece of Plexiglas (polymethylmethacrylate) was coatedwith a stock solution of p-amino benzoato chromic chloride as in Example16. The sample was dried at 70 C. for minutes, washed, dried again,immersed in the palladium chloride solution of Example 1 for 5 minutesand washed. Next, the sample was immersed in the nickel bath describedin Example 16, kept at 40 C. and metallic nickel started to deposit in10 minutes. Coating the Plexiglas sheet with a stock solution of p-nitrobenzoato chromic chloride or 3,4,5-trimethoxy benzoato chromic chlorideand treating it as the sample previously described, the same result isobtained.

Example 20.A piece of Pyrex glass and a piece of lime glass were coatedwith a solution of VOLAN (methacrylato chromic chloride) supplied by E.I. du Pont de Nemours & Co. The stock solution was diluted with water ata ratio of 1 to 3 and the pH of the resulting solution was raised to 5by the addition, under strong agitation, of a 1% morpholine solution inwater. The samples were dried for 20 minutes at 90 C., washed and driedagain. Next, they were immersed in the stannous chloride solution ofExample 1 for 2 minutes, washed with water, immersed in the palladiumsolution of the same example for 3 minutes, washed with water again andimmersed in the nickel bath of Example 16 kept at 40 C. Metallic nickelstarted to deposit in minutes and a very good nickel union was obtained.

Example 21. cc. of a stock solution of Quilon C as supplied by E. I. duPont de Nemours & Co., was diluted with an equal amount of Water. Astrip of paper was immersed in this solution and dried at 80 C. Next,the sample was washed with water and dried again. A hydrophobic coatingon the surface of the treated paper results. This strip of paper was,subsequently, immersed for 3 minutes in a palladium chloride solution,washed, immersed in the copper solution indicated in Example 5. Adeposition of metallic copper film with a resistance of 0.7 ohms persquare was obtained in 10 minutes.

Example 22.A strip of white organdy (cotton fiber) was immersed in thesame Quilon C solution and treated with the same process. Afterpalladium chloride sensitization, the sample was immersed in the coppersolution described in Example 5. Sound, metallic copper was deposited oneach thread of the textile in 15 minutes.

Example 23.A piece of white nylon (polyester) cloth was immersed in ap-amino benzoato chromic chloride stock solution that was diluted withequal parts of water. The sample was dried at 110 C. for 5 minutes,washed, dried again and immersed in the palladium chloride solution ofExample 1 for 3 minutes. With the immersion in the copper bath describedin Example 5 a deposition of sound, metallic copper on each thread wasobtained in 29 minutes.

Example 24.A piece of Teflon tape was immersed in a solution of p-aminobenzoato chromic chloride stock solution that was diluted with equalparts of water. The

sample was dried at 130 C. for 10 minutes, washed, dried again andimmersed in the palladium chloride solution of Example 1 for 3 minutes.With the immersion in the copper ibath described in Example 5, adeposition of sound, metallic copper was obtained in 30 minutes.

Example 25.One hundred volumes of styrene monomer 12-T (Dow ChemicalCo.) was washed with volumes of 20% aqueous sodium hydroxide. After several washings with vigorous agitation, the monomer was washed withdistilled water until no more caustic was obtained in the wash waterand, next, dried over anhydrous calcium sulfate for several hours atroom temperature. The monomer was next bulk polymerized by heating it ina closed glass vessel for 160 hours at 130 C. The polymer was dissolvedin tetrahydrofuran, dried, dissolved as follows:

Percent Xylene 42.5 Toluene 7.5 Methyl ethyl ketone 10 Methyl n-propylketone 10 Polymer 30 a film was formed by evaporating the solvent from athin layer of this material. The thus formed film was coated by dippingin a stock solution of p-amino benzoato chromic chloride diluted withwater in the ratio 1:1, dried in an air circulating oven at 60 C. for 5minutes, washed and dried again. Subsequently it was immersed in apalla- At 30 C. a deposit of metallic palladium was obtained in 2 /2hours. At 60 C. deposition of metallic palladium was obtained in 40minutes.

Example 26.A polystyrene film made as described in Example 25 wasimmersed in a stock solution of p-nitro benzoato chromic chloridesolution, dried in an oven at 60 C. for 3 minutes, washed, dried againand immersed in the following silver solution for 3 minutes:

AgNO g 45 NH OH 38% cc.. 32 H O cc 468 The sample was next washed withwater and immersed in the solution of Example 5. Sound, metallic copperdeposited in 15 minutes.

Example 27.-Clear films of nitrocellulose were obtained by evaporationof solvent from nitrocellulose solutions so formulated:

Grains Hercules N.C. RS 25-30 cps. 20 Butyl acetate 20 Xylene, 42.5%;Toluene, 7.5%; Methyl ethyl ketone,

10%; Methyl n-propyl ketone, 10%; Isopropyl alcohol, 15%; N-butylalcohol, 15%

Clear films were cast, by evaporation of the solvent, from thissolution. Stock solutions of:

p-Nitro benzoato chromic chloride Beta-resorcylato chromic chloridep-Amino benzoato chromic chloride 3,4,5 trimethoxy benzoato chromicchloride Volan were diluted with water to 1:1 and the films wereimmersed in each of these solutions and dried in an air circulating ovenat 60 C. for 5 minutes. Next, they were washed with water, dried againand immersed in the palladium chloride solution of Example 1 for 3minutes. After washing with water, the samples were immersed in thecopper bath described in Example 5. A deposition of sound, metalliccopper was obtained in 10-15 minutes in each instance.

What is claimed is:

1. In the method of electroless plating wherein a nonconductingsubstrate is sensitized, activated and plated with a metal in anelectroless plating solution, the improvement comprising treating saidsubstrate with a 7 Werner-type complex of chromium and polymerizing thesame prior to sensitization.

2. The process of claim 1 wherein the complex is dried on the surface ofa substrate.

3. The process of claim 1 wherein the Werner complex has a pH of fromabout 3 to 5.

4. The process of plating a metal on a nonconducting substratecomprising the steps of:

(a) wetting the substrate with a solution of a Wernertype chromiumcomplex (b) causing said complex to polymerize (c) treating saidsubstrate with a sensitizer solution, said sensitizer comprising aneasily oxidized metal salt (d) treating said substrate with anactivator, said activator being a salt of a noble metal (e) treatingsaid substrate with an elcctrolcss plating solution. 5. The method ofclaim 1 wherein the Werner complex is beta-resorcylato chromic chloride.

6. The process of claim 1 wherein the Werner-type complex is 3,4,5trimethoxybenzoato chromic chloride.

7. The process of claim 1 wherein the complex is stearato chromicchloride.

8. The process of claim 1 wherein the complex is pamino benzoato chromicchloride.

9. The process of claim 1 wherein the complex is methacrylato chromicchloride.

10. The process of electroless plating comprising the steps of (a)treating a nonconducting substrate with a solution of a Werner-typechromium complex (b) drying said chromium complex solution on thesurface of said substrate (c) treating said substrate with a stannouschloride sensitizer (d) treating said substrate with a palladiumchloride activator (e) immersing said substrate in an electrolessplating bath whereby a metal is deposited on the surfaces of thenonconducting substrate.

References Cited UNITED STATES PATENTS 2,791,515 5/1957 Nack 117-126XRALPH S. KENDALL, Primary Examiner.

1. IN THE METHOD OF ELECTOLESS PLATING WHEREIN A NONCONDUCTING SUBSTRATEIS SNESITIZED, ACTIVATED AND PLATED WITH A METAL IN AN ELECTROLESSPLATING SOLUTION, THE IMPROVEMENT COMPRISING TREATING SAID SUBSTRATEWITH A WERNER-TYPE COMPLEX OF CHROMIUM AND POLYMERIZING THE SAME PRIORTO SENSITIZATION.